An "overwhelmed" Miriam O'Reilly was tonight celebrating victory over the BBC after a tribunal ruled that the corporation was guilty of ageism in axing her from its flagship rural affairs show, Countryfile.

The tribunal found that O'Reilly, 53, was dropped because of her age and victimised by management who blamed her for newspaper stories criticising the corporation for dropping middle-aged women presenters.

The judgment is a blow for the BBC, which is likely to face a six-figure damages payout. It is the first time an age discrimination case has been upheld against the corporation, which apologised to O'Reilly and promised an immediate overhaul of how it recruits and appoints its presenters.

After the tribunal judgment, O'Reilly said: "I'm sorry, I swore I wasn't going to cry but I feel overwhelmed by this victory." She said ageism was "endemic" in television and "part of the culture of broadcasting". She described the verdict as "historic". "I felt I was treated badly because of my age and taking on the BBC was the right thing to do, however hurtful and stressful it has been," she said.

"I think broadcasters now realise that we are not going to take it. If you lose your job because of your age and not because you can't do it, it's a disgrace, it shouldn't be happening. After more than 25 years with the BBC I deserved to be judged on my ability and not on my appearance. I don't think having wrinkles is offensive."

The BBC has been rocked by a string of claims that presenters were replaced because they were too old, including Arlene Phillips, who was axed as a judge on BBC1's Strictly Come Dancing, and the newsreader Moira Stuart, who was dropped from the BBC in 2007. Both have returned to the corporation in new roles.

O'Reilly took the BBC to an employment tribunal after she was one of four female presenters, all in their 40s or 50s, who were dropped as part of a revamp of the show when it moved to a new primetime slot. The new-look Countryfile was broadcast for the first time in April 2009, with Julia Bradbury and Matt Baker, both in their 30s, joining 70-year-old veteran presenter John Craven. O'Reilly was dropped, along with fellow presenters Michaela Strachan, Juliet Morris and Charlotte Smith.

Broadcasters predicted the ruling would make it much harder for television executives to make arbitrary decisions about talent. Dawn Airey, the former senior Channel 5, ITV and BSkyB executive, who is an honorary member of the campaigning organisation Women in Film & Television, said the issues of age and sex discrimination were still "very live" for all broadcasters.

"This is a landmark ruling if the BBC changes some of its practices," said Airey. "It will be interesting to see how the BBC and the whole industry reacts to this. It's a very live issue for all broadcasters. It's a question of reflecting diversity on-screen, and if you don't reflect that then you're out of touch with viewers."

Airey added that TV producers and commissioning editors now had a "very hard balance to pull off" in recruiting and retiring on-screen talent. "[Presenters] always need to be given a valid explanation as to why [they're] moving on. But what's interesting from this case is that now you can't make that decision on the basis of age. It's a judgment call."

The finding is an embarrassment for BBC1's former channel controller Jay Hunt and the BBC director general, Mark Thompson, who became chair of TV industry body the Cultural Diversity Network just last week. Hunt began her job as Channel 4's chief creative officer on Monday.

The tribunal found that discrimination against O'Reilly "was not justified" and that she had been "dismissed almost entirely out of hand" along with two other Countryfile presenters. "The wish to appeal to a primetime audience, including younger viewers, is a legitimate aim. However, we do not accept that it has been established that choosing younger presenters is required to appeal to such an audience," the judgment stated.

Hunt's evidence to the tribunal contradicted that of the BBC's head of rural affairs, Andrew Thorman, who said she had sealed the fate of O'Reilly and two of the other female presenters dropped from the show in just eight words ("I think their experience is mainly radio, no").

Hunt also denied a suggestion that she "hated women". She said it was "categorically untrue and profoundly distressing and utterly offensive on every level".

The tribunal ruled: "Unfortunately we have come to the conclusion the inconsistencies in the evidence … arise not as a result of memories fading with time … but because they were not straightforward as to the real basis for their decision."

The verdict, which upheld O'Reilly's claim for age discrimination and victimisation but not sex discrimination, gives her the opportunity to claim damages including loss of earnings, injury to feelings and aggravated damages.

Her legal team said she would not be pursuing aggravated damages. The total damages the BBC will pay is likely to be in the low six figures. O'Reilly has earned £500 in the past year and has not worked for Countryfile since its relaunch nearly two years ago.

O'Reilly, who became a familiar voice on BBC Radio 4 presenting environmental programme Costing the Earth as well as Woman's Hour and Farming Today, is now considering offers of a return to the BBC. She indicated that she would like to return to Woman's Hour.

An award-winning journalist, she rejected an opportunity to settle with the corporation before the tribunal began last year. It is understood the BBC offered her a substantial sum, believed to be between £75,000 and £100,000, not to take the case to the tribunal.

In light of the tribunal's ruling, the BBC said it would give additional training to senior editorial executives and issue new guidance on the fair selection of presenters. The findings "raise questions that need to be addressed by the whole industry", the corporation said in a statement. The BBC said it was "committed to fair selection" and "clearly did not get it right in this case".